As a result of the effect of ozone, or ultraviolet irradiation the fluorescence of 3,4-benzopyrene decreases with increasing time of treatment, i. e. with increased amount of ozone introduced into the samples. At the same time the ultraviolet absorption peaks decrease too. If the treatment continues long enough the fluorescence is extinguished altogether. According to the measurements the fluorescence intensity versus time of the ozone treatment obeys a hyperbolic law.